Your ID has not been certified to access the server
What happened
The server you tried to access doesn't have a certificate in common with your User ID, so you were denied access to that server. Your User ID and the server's ID need to be certified by a certifier you both trust.
Note: You may see this message even if you're only editing a
mail message locally while waiting to get your new certificate(s)
back. If you choose View > Refresh while your cursor is
in the To: field, or you click Address, Notes® tries
to interpret the mail address you have entered.
What you can do
Ask the Notes® certifier if your User ID can be recertified so that you can access the server. Then choose File > Security > User Security, click , and then the Get Certificates button. Once the certifier (who may or may not be your HCL Domino® administrator) has returned your User ID with the new certificate attached, you'll be able to use the server.